When extruding hydraulic or non-hydraulic binding compositions, for example cement based pasty materials obtained by mixing inorganic particles with water and auxiliary components, in order to manufacture articles like cement profiles the problem of crack formation may arise leading to articles suffering from having a smooth surface.
JP1294555A is directed to an admixture for extrusion molded articles of cement and addresses the phenomenon and problem of dehydration when extrusion molding aqueous kneaded material whose main constituent is cementitious material leading to extrusion failure. As a solution for this phenomenon a cementitious admixture is provided comprising one or more of various alkycellulose ether and hydroxyalkyl alkycellulose ether having a particle size of not more than 100 μm wherein at least 50% by weight have not more than 50 μm. Furthermore, these cellulose ether have a degree of polymerization in the range of 200 to 1500.
Today cellulose ethers like hydroxypropyl methylcellulose (HPMC) and/or cellulose ether having a very low particle size are used as auxiliary compounds in extrudable compositions. These cellulose ethers are relatively expensive either as such or due to costly grinding procedures after production.
Therefore, the problem addressed by the invention was to provide an extrudable hydraulic or non-hydraulic binding composition, e.g. based on cement or gypsum or lime or hydrated lime, having improved properties with respect to crack formation using lower priced means than HPMC's and/or very fine grinded cellulose ethers. A further problem addressed by the invention was to provide a method of decreasing or avoiding the formation of cracks of an extruded hydraulic or non-hydraulic binding composition.